As an integrated circuit and the function of a computer are improved, a new application requiring a function for storing large amount of data has been being developed. There is an application requiring a nonvolatile semiconductor memory device having a function for electrically programming data and erasing stored data. Many applications become applicable by lowering the cost of making a nonvolatile semiconductor memory device per megabyte to less than one U.S. dollar. For example, there are alternative applications for
(1) a chemical film for storing a photographic image (photographic film),
(2) a compact disk (CD) for storing music data and text data for distribution,
(3) a digital versatile disk (DVD) for storing video data and multimedia data for distribution, and
(4) a magnetic tape such as a digital audiotape and videotape for storing audio and video data by audience.
The above conventional memory medium is a nonvolatile memory and stored in an archive (a storage case and the like) and can be removed from a main device and all power supplies for about ten years or more while the information recorded therein is kept so as not to be completely destroyed substantially. The nonvolatile semiconductor memory device is required to hold its data over a long period of time as with the CD, DVD, magnetic tape and almost all types of photographic films.
A nonvolatile semiconductor memory device that can be substituted for the conventional memory medium is a flash memory, EEROM and the like in which data can be electrically erased and programmed as of the moment. Unfortunately, according to the nonvolatile semiconductor memory device at present, memory cells are arranged on a monocrystalline silicon substrate two-dimensionally in general, and confined to a two-dimensional memory cell array. Therefore, the data amount that can be stored (memory capacity) is limited to the number of memory cells that can be formed in a single plane of the silicon substrate.
Meanwhile, according to a three-dimensional semiconductor memory device, since memory cell arrays are laminated on the substrate surface vertically, memory capacity per unit area is increased and the manufacturing cost per bit can be reduced. A three-dimensional semiconductor memory device disclosed in the following non-patent document 1 is a 3D-OTP (one time programmable) nonvolatile memory device in which memory cell arrays are laminated on a substrate surface vertically. Cross-point type memory cell arrays in which memory elements are disposed at intersection points of word lines and bit lines are laminated vertically to provide a four-layer structure.
According to the non-patent document 1, the film of the memory element is formed of polycrystalline silicon. A memory cell area per bit is 4F2. Here, “F” designates a minimum design dimension defined by a manufacturing process to be used. The memory cell area is equal to that of a flash memory having the same design rule. However, since the memory cell arrays have the four-layer structure in the three-dimensional semiconductor memory device, an effective cell area is 1F2 that is a quarter of 4F2. Therefore, the manufacturing cost can be reduced as compared with the flash memory. Each memory cell constituting the memory cell array is formed such that a state change part called “anti-fuse” and a selection part made up of a diode are connected in series and the ends of the memory cell are connected to a word line and a bit line, respectively. The anti-fuse is made of a silicon oxide film, and the diode is formed by laminating P-type silicon and N-type silicon. Data is stored using the resistance change of the anti-fuse when a voltage is applied to the memory cell. The anti-fuse is in a high insulating state initially and changed into a conductive state when the threshold voltage or more is applied. When the anti-fuse becomes the conductive state once, since it does not return to the insulating state, programming can be performed only one film. The diode is provided to prevent the current flowing in the selected memory cell from leaking.
Meanwhile, as the memory cell that can be employed in the cross-point type memory cell array in which two-terminal structured memory cells are arranged at the intersection points (cross points) of the word lines and the bit lines, various kinds of nonvolatile memory cells can be used other than the above anti-fuse provided with the diode regardless of whether the memory cell array has the two-dimensional structure or the three-dimensional structure. For example, it includes a memory cell formed of a transition metal oxide such as PrCaMnO or NiO that changes its resistance by an electric stress disclosed in the following non-patent document 2 and non-patent document 3, or formed of a phase change material such as GeSeTe that changes its phase by a thermal stress caused by a current disclosed in the following non-patent document 4, and a memory cell in which the above memory element material and a diode are connected in series.    Non-patent document 1: Feng Li et al., “Evaluation of SiO2 Antifuse in a 3D-OTP Memory”, IEEE Transactions on Device and Material Reliability Vol. 4 No. 3 (2004) pp. 416-421    Non-patent document 2: W. W. Zhuang et al., “Novell Colossal Magnetoresistive Thin Film Nonvolatile Resistance Random Access memory (RRAM)”, IEDM Technical Digest, pp. 193-196, December 2002    Non-patent document 3: I. G. Beak et al., “Highly scalable non-volatile resistive memory using simple binary oxide driven by asymmetric unipolar voltage pulses”, IEDM Technical Digest, pp. 587-590, December, 2004    Non-patent document 4: S. J. Ahn et al., “Highly manufacturable high density phase change memory of 64 Mb and beyond”, IEDM Technical Digest, pp. 907-910, December 2004